Bahrain has arrested at least 60 Shiite protest leaders in recent days to try to prevent widespread unrest ahead of the country's controversial Formula One Grand Prix this week.

News of the crackdown coincided with a statement from Amnesty International, which said it was getting credible reports of the use of torture in the Gulf Arab state, despite promises of reform.

"The authorities are trying to portray the country as being on the road to reform, but we continue to receive reports of torture and use of unnecessary and excessive force against protests," Hassiba Hadj Sahraoui, Amnesty International's Middle East and North Africa deputy director, said in a statement.

"Their reforms have only scratched the surface."

Bahrain is gearing up to host the Grand Prix on April 20-22.

The event was cancelled last year because of unrest.

Bahrain's government hopes the race will improve its international image and show it is serious about reform.

In particular, it is eager to show its Sunni Muslim rulers have repaired relations with the majority Muslim Shiite community after last year's protests, which were put down with the help of troops from neighbouring Saudi Arabia.

Bahrain's Shiites complain they are given fewer opportunities and access to jobs and housing than the Sunni elite.

But activists said on Tuesday relations between the two communities were still badly strained by routine violence.

They said riot police had used live ammunition for the first time since last year's pro-democracy protest movement was crushed, firing bullets into the air.

"We have evidence in photographs and video from April 13 in Diraz and Sitra," said Mohammed al-Maskati, head of the Bahrain Youth Society for Human Rights.